An Evolved Universal Mobile Telecommunications System (E-UMTS) based on an asynchronous mobile communication system standard (3GPP) transmits and provides a variety of data and services. For example, there are system information via a BCH (broadcast channel), control message via a PDCCH (physical downlink control channel), user traffic or control message via a downlink SCH (shared channel) or an uplink SCH (shared traffic or control message of broadcast/multicast service (MBMS) via a downlink SCH or a downlink MCH (multicast channel), initial uplink control message via a RACH (random access channel) and the like.
The MBMS (multimedia broadcast multicast service) is a sort of a broadcast/multicast service and is the service that simultaneously transmits data packets to a service that simultaneously transmits data packets to a plurality of user equipments (UEs). In this disclosure, ‘broadcast/multicast service’ can be replaced by one of different terminologies including ‘MBMS’, ‘point-to-multipoint service’, ‘MBS (multicast and broadcast service’ and the like. In the MBMS based on IP multicast, UEs share resources required for data packet transmission and receive the same multimedia data. Hence, in case that a UE at a predetermined level, which uses MBMS, exists in the same cell, it is able to raise resource efficiency. As the MBMS has nothing to do with an RRC connection, a UE in an idle mode can be provided with the service.
There are two kinds of MBMS operation modes, i.e., a broadcast mode and a multicast mode. The broadcast mode allows a single transmitter to transmit data to all receivers in the same sub-network. The multicast mode allows one or more transmitters to transmit data to one or more specific receivers. In the multicast mode, an intention to receive data needs to be delivered to a network and subscription and leaving is available.
In order to efficiently manage the broadcast/multicast service, it is necessary to check the number of UEs that attempt to receive a specific service. This kind of information is usable in determining an optimal scheme for providing the broadcast/multicast service. For instance, if the small number of UEs are interested in the corresponding service, it may be more efficient to use a separate dedicated channel to provide the service to each of the UEs. On the contrary, if a plurality of UEs are interested in the corresponding service, it may be more efficient to use a common channel.
A method for counting a UE which desires to receive a specific broadcast/multicast service (hereinafter referred to as ‘MBMS counting’) is initiated when an access information message is transmitted to the UE via a MCCH. If the UE attempting to receive the service is in an RRC connected state, counting can proceed using a dedicated channel or a RACH. On the other hand, if a UE is in an idle mode, an RRC connection request message is transmitted in accordance with a random access procedure using a RACH.
In the following description, the RACH and a random access procedure in WCDMA system are explained. First of all, a RACH is used to transmit data of a short length in uplink. And, such an RRC message as an RRC connection request message, a cell update message, a URA update message and the like is transmitted via the RACH. A logical channel such as CCCH (common control channel), DCCH (dedicated control channel) and DTCH (dedicated traffic channel) can be mapped to the RACH which is a transport channel. And, the RACH is mapped to a physical random access channel (PRACH).
Once a MAC (medium access control) layer of a UE indicates a PRACH transmission to a physical layer of the UE, the physical layer of the UE selects a single access slot and a single signature and then transmits a PRACH preamble in uplink. The preamble is transmitted for an access slot interval having a length of 1.33 ms. One of 16 kinds of signatures is selected and transmitted for a first predetermined length of the access slot. If the UE transmits the preamble, a base station transmits a response signal via a downlink physical channel which is a AICH (acquisition indicator channel). The AICH transmitted as a response for the preamble carries the signature selected by the preamble for a first predetermined length of an access slot corresponding to the access slot for transmitting the preamble. In this case, the base station transmits a positive response (ACK: acknowledgement) or a negative response (NACK: non-acknowledgement) to the UE using the signature carried by the AICH. If the UE receives ACK, it transmits an RRC connection request message to the network using an allocated radio resource. Thereafter, the network transmits a contention resolution message and an RRC connection setup message to the UE. If the UE receives NACK, it indicates a PRACH transmission to the physical layer of the UE again after an appropriate duration. Meanwhile, if the AICH corresponding to the preamble transmitted by the UE is not received, the UE transmits a new preamble by a power 1-step higher than that of the previous preamble after a predetermined access slot.